Fuel rails for supplying fuel to fuel injectors of internal combustion engines are well known. A fuel rail is essentially an elongate fuel manifold connected at an inlet end to a fuel supply system and having a plurality of ports for mating with a plurality of fuel injectors to be supplied.
Fuel rail systems may be recirculating, as is commonly employed in diesel engines. Fuel rails are more typically “returnless” or dead ended, wherein all fuel supplied to the fuel rail is dispensed by the fuel injectors.
A well-known problem in fuel rail systems, and especially in returnless systems, is pressure pulsations in the fuel itself. It is known that fuel system damping devices are useful in controlling fuel system acoustical noise and in improving cylinder-to-cylinder fuel distribution. Various approaches for damping pulsations in fuel delivery systems are known in the prior art.
For a first example, one or more metal spring diaphragm devices may be attached to the fuel rail or fuel supply line. These provide only point damping and can lose function at low temperatures. They add hardware cost to an engine, complicate the layout of the fuel rail or fuel line, can allow permeation of fuel vapor, and in many cases simply do not provide adequate damping.
For a second example, the fuel rail itself may be configured to have one or more relatively large, thin, flat metal sidewalls which can flex in response to sharp pressure fluctuations in the supply system, thus damping pressure excursions by energy absorption. This configuration can provide excellent damping over a limited range of pressure fluctuations but it is not readily enlarged to meet more stringent requirements for pulse suppression.
For a third example, a fuel rail may be configured to accept an internal damper comprising a sealed metal pillow typically having a flat oval cross-section and formed of thin stainless steel. Air or an inert gas is trapped within the pillow. The wall material is hermetically sealed and impervious to gasoline. Such devices have rigid sidewalls supporting and separating relatively large, flat or nearly-flat flexible diaphragm sides that can flex in response to rapid pressure fluctuations in the fuel system. The flexing absorbs the energy of the pressure spike and reduces the wave speed of the resultant pressure wave, thereby reducing the amplitude of the pressure spike. Internal dampers have excellent damping properties, being easily formed to have diaphragm-like walls on both flat sides, and can be used in rails formed of any material provided the rail is large enough to accommodate the damper within. An internal damper may be advantageous over the wall-formed damper, in that mechanical failure of the damper results only in flooding of the damper itself and not in an external fuel leak.
The damping characteristics of a prior art internal damper are a function of the thickness of the diaphragm wall, the total wall area, the volume of captive air, and the mechanical characteristics of the metal. To increase the damping capability of an internal damper by applying prior art technology requires an increase in the captive air volume, a thinner wall, or increased area of the walls.
Reducing wall thickness is not desirable because it reduces the functional margin between stress and yield. Increasing the diaphragm wall area is feasible provided that a) the resulting damper is flexible enough to achieve the desired minimum change in volume for a given change in pressure without approaching the material yield point; b) the resulting damper will withstand cyclic fatigue; and c) the resulting damper is still small enough to fit into the fuel rail. Increasing the size of a fuel rail to accommodate a damper having a larger diameter or longer length is highly undesirable because the space adjacent the engine in a vehicle is already highly congested and limited, and because a new fuel rail design or layout increases the cost of manufacturing an engine.
The damping response of a prior art metal damper is essentially linear and has a limited linear range of response. Thus, a damper having excellent low-amplitude damping characteristics also has a relatively short range of amplitude-damping response capability. What is needed in the art is a fuel rail internal damper that can be tuned to meet fuel system pressure requirements having a variable, non-linear, and progressive stiffness to accommodate a greater range of pressure fluctuations in a given damper volume.
It is a principal object of the present invention to provide a greater range of pulse amplitude-damping capability in a fuel rail internal pulse damper while requiring no change in the size of a fuel rail accepting the damper.